One type of gene therapy of tumors, gene-directed enzyme-prodrug therapy (GDEPT), holds considerable promise, although practical considerations limit its clinical applicability. These include the lack of acceptable noninvasive methods that are adaptable to humans for selective tumor targeting of the therapeutic genetic material. Sindbis virus is an oncolytic, alphavirus that selectively targets tumors through the 67-kDa laminin receptor (LAMR).
Gene therapy targets the genome of tumor cells as a basis for a highly selective and nontoxic anticancer therapy. To enhance selectively and specificity to the killing of cancer cells, several enzyme/prodrug systems—such as carboxylesterase/CPT-11 (1), cytosine deaminase/5-fluoro-cytosine (2), and herpes simplex virus thymidine kinase type 1 (HSVtk)/ganciclovir (GCV) (3,4)—have been developed for gene-directed enzyme-prodrug therapy (GDEPT). In this strategy, tumor cells are transduced with therapeutic genes that encode enzymes for specific conversion/activation of prodrugs, which are toxicologically inert at relatively high doses, into highly toxic metabolites for tumor killing.
In addition to a proper vector system, cancer GDEPT therapy would greatly benefit from a means to noninvasively monitor the GDEPT enzyme activity after vector treatments in vivo. Such capability could improve the Sindbis-based HSVtk/GCV GDEPT in clinical settings by providing important information to address 2 critical questions: (i) Do the vectors systemically target tumor cells and spare normal tissues? (i) Do the tumors have sufficient expression levels of the enzyme for tumor eradication by subsequent prodrug activation? In addition, monitoring during the therapy could facilitate optimizing the dose and dosing schedule of the prodrug to reduce unwanted side affects.
U.S. Pat. No. 7,306,712 discloses that vectors based on Sindbis virus, a blood-borne alphavirus transmitted through mosquito bites, infect tumor cells specifically and systemically throughout the body. The tumor specificity of Sindbis vectors may be mediated by the 67-kDa high-affinity laminin receptor (LAMR), which is over expressed in several types of human tumors. Another advantageous property of Sindbis vectors for cancer therapy is that, without carrying cytotoxic genes, they have been shown to induce apoptosis in mammalian cells. Furthermore, as Sindbis vectors are capable of expressing very high levels of their transduced suicide genes in infected tumor cells, the efficient production of the enzymes for sufficient prodrug conversion is ensured.
U.S. patent application Ser. No. 10/920,030 discloses methods and compositions for detecting cancer cells and monitoring cancer therapy using replication defective Sindbis virus vectors.
U.S. Pat. No. 7,303,798 discloses novel defective Sindbis virus vectors and their use in treating tumors in mammals.